Fragment modes

The dominant fragmentation mode of pyrimidine is loss of HCN twice, to give ionized acetylene, m/e 26, as base peak whether C-2 or C-4 is involved in the initial loss of HCN... 

Both fragmentation modes are apparent in the mass spectrum of 1-butanol (Figure 17.14). The peak at ni/z = 56 is due to loss of water from the molecular ion, and the peak at mjz = 31 is due to an alpha cleavage. 

Harvey, D.J. Naven, T.J.P. Ktister, B. Bateman, R. Green, M.R. Critchley, G. Comparison of Fragmentation Modes for the Structural Determination of Complex Oligosaccharides Ionized by MALDl-MS. Rapid Commun. Mass Spectrom. 1995, 9, 1556-1561. 

Pavines which have nonidentical substituents on rings A and D furnish two different isoquinolinium ions through the same fragmentation mode, as ex-... 

The fragmentation mode of pyridine itself involves initial loss of HCN from the molecular ion (67CC1129). Deuterium labelling shows that this process is preceded by randomization... 

A significant fragmentation mode of the A-alkylpyrroles produces an ion of mass 67 which is almost homogeneous and corresponds to C4H5N+. Deuterium labeling has established that this ion arises predominantly by hydrogen migration either from C-4 of the alkyl... 

The mass spectra of ethyl polymethylpyrrole carboxylates are little affected by the orientation of the methyl groups and ester groups. Peaks resulting from fragmentations of the type shown in Scheme 6 remain unchanged in their relative size, but the relative abundance of the peaks originating from fragmentation modes in which the methyl... 

The observed reactivity towards nitrogen indicates a possible dissociation of the dimeric molecule into monomeric fragments, with one conceivable fragmentation mode indicated in Equation 1. 

This fragmentation mode is not altered for silacyclobutanes bearing a vinyl group at the silicon17, as the same Arrhenius parameters are found for the decomposition of 1 and of 1 -methyl-1-vinylsilacyclobutane 3 (logA = 15.64 s 1, E = 62.6 kcalmol-1), in sharp contrast to the pyrolysis of cyclobutanes where a vinyl group accelerates the pyrolysis by a factor of nearly 60018. 2-Silabuta-l,3-diene 4 was produced in a laser-photosensitized (SFg) decomposition (LPD) of 1-methyl-1-vinylsilacyclobutane 3... 

Dehydrotelobine (123), C35H32N205, was obtained from the bark of Daphnandra apatela Schodde (Monimiaceae). The NMR spectrum shows great similarity to that of telobine (78), but the UV spectrum ( max 336 nm) indicates a more conjugated system. The alkaloid also has only a weak MS m/e 335 (corresponding to cleavage at a, a major fragmentation mode in reduced alkaloids such as... 

D. J. Harvey, T. J. P. Naven, B. Kiister, R. H. Bateman, M. R. Green, and G. Critchley, Comparison of fragmentation modes for the structural determination of complex oligosaccharides ionized by matrix-assisted laser desorption/ionization mass spectrometry, Rapid Commun. Mass Spectrom., 9 (1995) 1556-1561. 

The fragmentation mode was observed mostly in electron-rich cyclic alkenes, including steroids, which afforded co-formyl nitriles [89] ... 

It happens that a common fragmentation mode for methyl phosphates is the loss of formaldehyde from the methoxyl group. If it can be shown that for one set of syn-isomers the m+ 1 parent ion loses [l60]formaldehyde to form a m + 1 daughter while the m+2 ion loses [l80]formaldehyde to form the m daughter and the m + 3 parent loses [nO]formaldehyde to form the m + 2 daughter, the (Sp) configuration... 

It was suggested that the formation of CH3T occurs directly via a different fragmentation mode of the excited alkanium ion ... 

Both of these characteristic fragmentation modes arc apparent in tt mass spectrum of l butanoI Figure JT.lSi. The peah at mfz 66 is duet loss of water from the molecular ion, and the peak aim/z 31 iaductoao alpha cleavage. 

IR spectroscopy is of limited practical use for distinguishing between species of types 3 and 5. Both exhibit absorptions typical of a bent metallocene unit (e.g., 3a p = 3100, 1440, 1020, 795 cm ) (55). In the mass spectrum, loss of the diene ligand to give Cp2Zr (m/e = 220) seems to represent the dominating fragmentation mode. The mutual rearrangement 3 5 can be followed in many instances by UV/visible spectroscopy. 

Polymerization rates were approximately half-order with respect to photoinitiator conrentration and first-order in monomer. A fragmentation mode for desyl aryl sulphides had previously been proposed by Schonberg et al. (29) who isolated bidesyl after prolonged exposure to sunlight of benzene solutions of these compounds ... 

The number of classes of compounds which can be grouped under the general heading of lipids is too large to allow their individual detailed consideration. Some have been more fully studied than others and are best treated separately e.g. prostaglandins, steroids. The MS fragmentation modes of fatty acids and esters have been discussed extensively in the past and are well summarised by Odham and Stenhagen [265]. A variety... 

---